Despite renewed interest during recent years, knowledge of the anatomy of the inner ear in lower vertebrates is still sharply limited. Thus, as a continuation and expansion of previous work, the primary objective of the project proposed is to contribute to the body of scientific information concerning the comparative anatomy (morphology, histology, cytology) and evolution of the vertebrate labyrinth by utilizing current techniques of light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The investigations proposed include: (1) a survey of auditory end organs in selected representatives of caudate and apodan amphibians; (2) investigation of the comparative occurrence of gap junctions in labyrinthine neuroepithelium from a selected series of reptiles; (3) investigation of the origin of calycine nerve endings in the vestibular neuroepithelium of reptiles; (4) study of the production of afferent synaptic vesicles in selected reptiles; and (5) an investigation of the histogenesis and cytogenesis of a vestibular end organ in the laboratory mouse.